For RIPE (don't know others) the are two ways: you can either sign up as a full member (an ISP) for 1500€/year, which gives you the same rights as any other ISP

For RIPE (don't know others) the are two ways: you can either sign up as a full member (an ISP) for 1500€/year, which gives you the same rights as any other ISP. You can also request a "provider independent" or PI address block, which comes with some contractual restrictions (you have to use it yourself and you can't act as an ISP), from a member for 50€/year plus their profit margin. Officially you should get one from your actual ISP, but there are a few RIPE members who sell easy access to PI blocks as part of their business model.